Home whitening kits are a popular way to turn a dull smile into a dazzling one. But these self-applied products only work for teeth with outer enamel stains — if the discoloration originates inside a tooth, you’ll need professional treatment.

Known as “intrinsic staining,” this type of discoloration most often occurs within a tooth’s pulp or dentin layers. There are a number of causes like tooth trauma or tetracycline use at an early age. A root canal treatment used to remove infection from deep within a tooth can also cause discoloration: sometimes blood pigments left after tissue removal or the filling materials themselves can stain a tooth’s interior.

Intrinsic staining can often be treated by placing a bleaching agent, usually sodium perborate, into the tooth’s pulp chamber. But before undertaking this procedure on a tooth that’s undergone a root canal treatment,Â we want to first ensure the filling is intact and still adequately sealing the tooth from infection. We also want to make sure the supporting bone is also healthy.

If all’s well, we access the pulp in the same way as the root canal treatment, and preferably through the same access hole. We then clean out the pulp chamber of any stained matter and then ensure the root canals remain filled and sealed off from the pulp chamber.

We can then place the bleaching agent into the pulp, a process that will need to be repeated every three or four days to achieve the desired level of brightness. After each session we place a cotton pellet over the opening and held in place with a temporary adhesive; we can easily remove and re-apply this covering during subsequent sessions. Once we’ve achieved the desired color change, we seal the tooth with a permanent filling and restore the access cavity with a tooth-colored composite resin material bonded to the enamel and dentin.

There are other options for an intrinsically stained tooth like veneers or crowns that outwardly cover the discoloration. Internal bleaching, however, is a more conservative approach that causes less alteration of the tooth. If successful, it can restore a stained tooth to a brighter, more attractive shade.